Yes, this can be a slippery slope and there is no one, air-tight answer. There are always a few moving parts to this situation; how, long dating, casual or LTR, her personality, her history, and most of all your intuition and gut feel. Based on my experience, here's how I've handled it. IDGAF and Abundance Mentality is the backdrop in all interactions.
-Casually mentions guy friends: "Cool, sounds like a good friend, have fun!" Don't show emotions. You don't care.
-Keeps bringing up a "friend" from work, social circle, etc.: This I have called them out on. Very casually and inquisitively I may say (but NOT angrily): "So that's the sixth or seventh time you're brought up Billy from work today. Maybe you two should date. Sounds like he's on you're mind a lot. Just let me know, it's cool." Then I change the subject. Tacitly you're sending IDGAF vibes AND saying shut the f*uck up but about Billy or you can have him because I'll be gone.
-Keeps bringing up her ex: I'll let this go a few times but if it became persistent, I may say, "That's the fifth time you've brought up your ex Johnny today. I really have no interest in what kind of meds he was taking for depression or anything else about him. I'd rather focus on you and me and plan some fun stuff." Then change the subject.
As a rule, you're better off NOT saying anything and just watching her actions. Any girl worth pursuing won't pull this crap. If they do, it's only for (all) bad reasons:
-low self esteem
-trying to make you jealous
-they DO have interest someone else
-low interest in you
-immature
-poor dating etiquette
Not a woman a DJ should take seriously.
High quality women may actually have beta platonic friends they don't want to bang (pretty common)--or they would be already--and not be with you. So just chill, and if she's playing with her orbiters and it's cutting into your fun time with her, keep your dignity intact, use IDGAF and AM, give her a chance to change her behavior, and if she doesn't or gets defensive, MOVE THE F*UCK ON.
Got it? Good.
~Dash